Precise visualization of catheters and real-time knowledge of their localization with respect to the anatomy are needed for minimally invasive interventions. Intra-operative ultrasound is often used for these purposes. However, many surgical tools are difficult to image with conventional pulse-echo ultrasound. For instance, the usability of 3D Transoesophagial Echocardiography (3D-TEE) for guidance of catheter cardiac interventions is still limited because it is challenging to image catheters reliably with ultrasound. Catheters are specular reflectors that reflect the sound away from the imaging probe if the insonifying angles are not favorable. As a consequence, a catheter appears on and off on 3D-TEE images during its progression through the cardiac chambers. It also frequently happens that some parts of the catheter are visible and others not depending on the local angle between the catheter and the imaging beams, for instance the distal end of the catheter may be invisible and some point along its shaft may be mistaken as its tip. Also, due to weak reflection, signal from the catheter may be drowned in signal from the surrounding anatomy.
Electromagnetic (EM) tracking sensors have been mounted aboard catheters for tracking their tip and other selected locations along their shaft. However, the positioning accuracy of such sensors can get really poor (of the order of 10 mm) in EM distorted operating environment. Additionally, an independent EM tracking system adds to the equipment cost and clutter in the catheter laboratory.
U.S. Pat. No. 4,249,539, entitled “Ultrasound needle tip localization system,” to D. H. R. Vilkomerson et al. (hereinafter “Vilkomerson”) discloses an active ultrasound transducer that is attached at the tip of a biopsy needle to be imaged by a B-mode ultrasound scanner. The transducer at the tip of the needle, upon sensing signals from the imaging probe, immediately transmits back a short pulse. The ultrasound transducer on the needle thus merely acts as a “super-reflector” that re-radiates a strong ultrasonic signal upon insonification. The imaging paradigm is not modified and the “super-reflector” is simply seen as a very bright point in the ultrasound image. Furthermore, all embodiments described in that patent results in a very bad lateral resolution of the needle tip because there is no proper transmit focusing.